Lids for closing off containers

ABSTRACT

Lids, for example lids for machine-lidding of e.g. beakers, dishes, menu dishes, goblets, small packages etc., containing a substrate material featuring, with respect to a container on which the lids are used, a smooth outward facing surface bearing printing. On the inward facing side of the lid is a sealing layer deposited by extrusion laminate coating. The sealing layer exhibits on the free surface embossing with a depth of roughness of up to 50 μm. The embossing is transferred to the sealing layer in the form of a roughness pattern on the cooling roll on depositing the laminate coating of the substrate material and extruded sealing layer. The free side of the substrate material is smooth and exhibits no embossing. Printing on the free surface is therefore of higher quality. The extruded sealing layer on the substrate material exhibits embossing on the free side. If the lids are drawn from a stack of lids, for example in a filling machine, the embossing allows them to be separated individually. The lids are suitable for closing off containers using a sealing seam in which the lids contain a substrate material featuring, with respect to a container on which the lids are used, outward facing printing and an inward facing sealing layer.

[0001] The present invention relates to lids for closing off containersusing a sealing seam in which the lids contain a substrate materialfeaturing, with respect to a container on which the lids are used,outward facing printing and an inward facing sealing layer.

[0002] It is known to provide containers such as deep drawn or stretchdrawn containers with a ring-shaped shoulder at their opening and to lidsuch containers, in particular after filling, such that the lid liesover the whole of the shoulder and e.g. by sealing or adhesive bonding,to attach the lid permanently and in an air-tight manner to theshoulder.

[0003] The lids are e.g. stamped out of an endless strip of lid materialand stacked. The stacks of lids are fed to a packaging machine and theindividual or unstacked lids continuously sealed on to the alreadyfilled containers. The lids—already featuring a sealing layer—are sealedonto the shoulder region of the container at the edge of the containerusing a sealing tool. The separation or unstacking of the lids from thestacks is not always reliably performed by the packaging machine as thestacked lids may stick to each other. It is possible to prevent the lidsfrom sticking together, for example by embossing the lid material.Embossed patterns on the lid material, however, have a negative effecton the printed image on the outside of the lid.

[0004] The lid material can be of various different materials dependingon the requirements in question. Typical examples of lid material aremetal foils which may be coated with plastic on one or both sides. Otherlid materials contain or comprise of plastics in the form of mono-filmsor multilayer laminates. Further lid materials can be ofcellulose-containing materials such as cellophane or paper. AlsoLaminates of metal foil and plastic films are employed. In order to sealthe lid material to the edge of the container, the lid material isprovided over the whole of its surface with a sealing layer such as anorganic coating or sealing film, whereby the sealing layer is depositedat least on the side of the finished packaging facing the inside i.e.facing the interior of the container.

[0005] The lid material also serves as a substrate for information andadvertising. For that reason the lid material is generally provided withprinting on its outside. The printing may be on the uppermost layerfacing outwards on the finished container i.e. so called first formprinting. The printing may also be covered over by a protective lacqueror a protective film, or the uppermost layer may be of transparentmaterial and bear the printing as a reverse image in the form ofcounter-printing. The printed images may be single or multi-coloured andmay be deposited in a printing machine.

[0006] Application of an embossed image is a disadvantage with known lidmaterials. The embossing is necessary in order that the lidsmanufactured from the lid material in stacks can be fed to the packagingmachine, and that the lids can even be separated piece for piece fromthe stack and sealed onto the container. As the lid material has to beembossed, the finished lid is at a disadvantage to reproduce the desiredimage.

[0007] The object of the present invention is to overcome thisdisadvantage and to propose a lid that can be separated into individuallids from a stack of lids, yet reproduces with high quality the image onits surface.

[0008] That objective is achieved by way of the invention in that thesealing layer on the free surface exhibits embossing with a depth ofroughness of up to 50 μm and the free surface of the substrate materialshowing the printing is smooth and is not embossed.

[0009] The depth of roughness is e.g. from 3 to 30 μm, usefully 3 to 20μm and advantageously 5 to 10 μm. The depth of roughness is inparticular not greater than the thickness of the sealing layer.

[0010] The sealing layer may be an extrusion layer or a co-extrusionlayer.

[0011] The sealing layer may contain a co-extrusion layer of a bondingagent and/or a primer and a seal-able thermoplastic. The bonding agentand/or primer lie on the substrate material and the sealablethermoplastic on the bonding agent and/or primer.

[0012] The sealing layer exhibits e.g. a weight per unit area of 30 g/m²and less, usefully from 2 g/m² to 20 g/m², advantageously from 2 g/m² to15 g/m², in particular from 5 g/m² to 10 g/m².

[0013] The sealing layer may be e.g. a co-extrudate with a bonding agentas extrusion layer having a weight per unit area of 2 to 10 g/m²,usefully from 2 g/m² to 8 g/m², and an extrusion layer of athermoplastic having a weight per unit area of 3 to 25 g/m², inparticular from 5 g/m² to 10 g/m².

[0014] The substrate material may be a monofilm of plastic or amultilayer composite made up of two or more plastic layers or a metalfoil or a multilayer composite of at least one metal foil and at leastone plastic film. The substrate material may also be comprised of acellulose-containing material or contain a cellulose-containingmaterial. The cellulose-containing material may be coated on one or bothsides with a plastic layer or be metallised or may exhibit on one side aplastic layer and a metallised layer on the other side. The plastics ofthe substrate material may be e.g. polyolefins such as polyethylenes orpolypropylenes, polyamides, polyethylene-terephthalates orpolyvinylchlorides. Steel or aluminium e.g. may be used as metal foils.Cellulose-containing materials that may be used are e.g. papers orsemi-cardboard. Further substrate materials are e.g. cellophane. Thesubstrate material may have a thickness e.g. of 12 to 500 μm, wherebythe substrate materials in the form of plastic films or metal foils ormetal foils and plastic films are preferably 12 to 150 μm thick, whilelid materials containing cellulose-containing materials are e.g. 40 to500 μm thick. The substrate materials are in particular flexible to suchan extent that they can be coiled into rolls.

[0015] The substrate material may also exhibit a barrier layer againstgases, vapours and moisture. Barrier layers may be—in addition to theabove mentioned metal foils—be e.g. of plastics such aspolyvinyliden-chloride or ethyl-vinyl-alcohol, or may be a layer ofceramic material such as the oxides or nitrides of silicon or aluminium,deposited in a vacuum deposition process onto a substrate film as a thinlayer e.g. in the thickness range of 10 to 500 nanometers. Examples offurther barrier layers are metal layers e.g. of aluminium deposited onthe substrate by sputtering.

[0016] Printing may be provided on the side of the lid which on thefinished container is the outward facing side. Such printing may beadvertising, competition or information in word form and/or imageform.The printing of the substrate material may be performed using all knownprinting methods such as e.g. typographic, offset, flexo, screen,heliographic and copper-plate printing. The choice as to which printingmethod is to be used depends on the quality of printing desired, on theprevailing technical aspects and the size of series to be printed.Preferred is flexo-printing (also known as aniline or rubber printing)and intaglio printing such as copper-plate, or helio printing. Theprinting on the outside of the substrate may be protected additionallye.g. by coating over with a protective lacquer or, using a laminatingagent or an adhesive, a transparent film—e.g. ofpolyethylene-terephthalate, polyamide, polyolefins such as polyethyleneor polypropylene or a cellophane layer which, however, in general inorder to protect the printed image is printed on by counter-printing—maybe laminated onto the substrate material. The printing may take place onthe substrate material or after depositing the sealing layer.

[0017] The non-printed material—as with the printed substratematerial—is in particular smooth and non-embossed or exhibits a smoothsurface without embossing. As a result the printing quality isunimpaired.

[0018] The sealing layer may contain or comprise a thermoplastic, forexample from the series of polyolefins, preferably polyethylenes orpolypropylenes or copolymers or terpolymers of ethylene e.g. copolymersor terpolymers of ethylene and acrylic acid (EAA, ethyl acrylic acid),of ethylene and acrylic esters such as methacrylate (EMA), ethylacrylate (EAA) or butylacrylate (EnBA), of ethylene and vinylacetates(EVA), of ethylene and methacrylic acid (EMMA), of ethylene andethylacrylate and acrylic acid (EAEAA) or ionomer resins, alone or inmixture form. The sealing layer may also contain one of theaforementioned thermoplastics and bonding agent or primer, for examplefrom the polyester or vinylpolymer series. The sealing layers maycontain or be made of e.g. polyesters or polyamides or their copolymersor terpolymers.

[0019] The present invention relates also to a process for manufacturinglids for closing off containers by means of a sealing seam, where thelid with reference to a container on which the lid is employed, containsa substrate material with outward facing printing and an inward facingsealing layer.

[0020] The process may be performed in such a manner that the substratematerial is coated, via extrusion coating or co-extrusion coating, withan extrusion layer (extrusion film) or co-extrusion layer (co-extrusionfilm) forming the sealing layer, and the coated substrate material ispassed between a pressure roll and a cooling roll while being put underpressure, whereby the substrate material faces the pressure roll and theextrusion layer or co-extrusion layer faces the cooling roll, and theconfiguration of the surface of the cooling roll transfers to theextrusion layer or co-extrusion layer i.e. the sealing layer as areverse image. For example the substrate material is uncoiled from aroll as an endless strip and passed over a pressure roll. The film orfilms of the sealing layer are produced in one or more extruder nozzlesin the region of the pressure roll. In order to improve mutual adhesion,the substrate material and/or the extrusion layer or layers may besubjected to flame, plasma, corona or ozone treatment. Under the actionof gravity the extruded film or films make contact with the substratematerial running continuously over the pressure roll. The contactsurface of the pressure roll is essentially smooth i.e. in particularnot embossed and without any roughness structure. The cooling roll isprovided in the device as counter roll to the pressure roll. The surfaceof the cooling roll is embossed. The substrate material coated with theextruded film or films passes between the pressure roll and the embossedcooling roll. The surface of the pressure roll is smooth or withoutembossing or the like and supports the substrate material, the freesurface of which also remains smooth while the cooling roll transfersits image onto the solidifying extrusion film i.e. the sealing layer.The result is a lid material one side of which, the substrate materialand printed side, is smooth and non-embossed while the other side viz.,the sealing layer side, exhibits a roughness pattern or embossing. Inother words the lid material or the lid according to the inventiontherefrom exhibits one on top of the other as the case may be, aprotective lacquer or a protective film, printing and/orcounter-printing, the actual substrate material and finally the sealinglayer comprising a layer of thermoplastic or a layer of bonding agentand/or primer and a layer of thermoplastic, where the free surface ofthe layer of thermoplastic exhibits the roughness pattern Used as a lid,the sealing layer in particular faces the interior of the container andthe printing faces out. By employing stamping or cutting methods, theindividual lids can be made from the lid material which can be coiledinto roll form. The lids may then be stacked for e.g. use in a fillingmachine.

[0021] The cooling roll preferably exhibits as surface configuration asurface roughness pattern having a roughness depth of up to 50 μm,usefully from 3 to 30 μm, advantageously from 3 to 20 μm and inparticular from 5 to 10 μm.

[0022] The roughness pattern on the cooling roll may e.g. be created bygrinding, spark erosion, embossing, blasting with hard materials etc.The roughness pattern should to advantage not exceed a depth ofroughness which is greater than the thickness of the sealing layer. Thismeans that the roughness pattern should not penetrate the sealing layerand the embossing should also not be transferred to the substratematerial. The roughness pattern on the cooling roll may take any formand may be a random pattern of recesses in the surface, it may be aworm-shaped embossing, damask-like embossing, line-shaped, stroke ordot-like pattern etc.

[0023] The lids according to the invention of a substrate materialwith—referring to containers on which the lids are used—outward facingprinting and inward facing sealing layer, find application in theclosure of containers that have a shoulder region, the lids beingattached via the sealing layer to the container in the shoulder region.Such containers are e.g. deep drawn or stretch drawn or cast, such asinjection moulded, containers, or otherwise shaped containers theopening in which feature a fiat ring-shaped shoulder. The containers arelidded, in particular after filling, and viz., such that the lid liesover the whole of the shoulder and is attached to the shoulder in anair-tight manner e.g. by sealing or adhesive bonding. Such beakers,dishes, menu-dishes e.g. such with a plurality of compartments, goblets,small forms of packaging etc. may be employed for packaging foodstuffsof all kinds such as e.g. milk products, in particular yoghurt, creamfor whipping, sour milk, sour cream, coffee cream, ready made meals, ofsalads or semi-conserved or fully conserved foodstuffs, precooked orotherwise prepared meals, drinks such as fruit juices and vegetablejuices, drinking water etc.

[0024] The lids in question may be sealed to the rim of the container bymeans of the sealing layer. The strength of the seal can be adjusted byappropriate choice of sealing tool, the sealing pressure and the sealingtemperature. Aids to tearing may be provided e.g. in the form of weakersealed regions at the seam, or by means of zigzag shaped edges to thesealing seams. Instead of sealing via the sealing layer, the bonding maybe effected using an adhesive such as a contact adhesive or an adhesivethat bonds under the action of heat and/or pressure.

[0025] The lid material presented here has the advantage that e.g. inorder to create the sealing layer in the form of an extrusion layer orco-extruded layer, it is not necessary to employ solvents that have tobe vaporised and recovered or destroyed. The embossing at the sealingseam prevents the lids from sticking together on being separated fromthe stack. As a result, the stacked lids according to the inventionhaving one smooth side and one embossed side may be used reliably inpackaging machines.

[0026] The finished lids may also feature a tear-off or gripping flapand/or weakness, e.g. in the form of perforations or tearing notcheswhich make it easier to open the container on removing the lid.

1. Lids for closing off containers using a sealing seam in which thelids contain a substrate material featuring, with respect to a containeron which the lids are used, outward facing printing and an inward facingsealing layer, characterised in that, the sealing layer on the freesurface exhibits embossing with a depth of roughness of up to −50 μm andthe free surface of the substrate material showing the printing issmooth and is not embossed.
 2. Lids according to claim 1, characterisedin that the depth of roughness is 3 to 30 μm, usefully 3 to 20 μm,advantageously 5 to 10 μm.
 3. Lids according to claim 1, characterisedin that the sealing layer is an extrusion layer.
 4. Lids according toclaim 1, characterised in that the sealing layer is a co-extrusionlayer.
 5. Lids according to claim 1, characterised in that the sealinglayer is a co-extrusion layer contains a bonding agent and/or a primerand a sealable thermoplastic.
 6. Lids according to claim 5,characterised in that the sealing layer contains sealable thermoplasticsfrom the polyolefin series, preferably polyethylenes or polypropylenes,copolymers or terpolymers of ethylene or polyester or polystyroles orpolyamides or their copolymers or terpolymers.
 7. Lids according toclaim 1, characterised in that the substrate material containsnon-embossed thermoplastics or a non-embossed cellophane or anon-embossed cellulose-containing material or a non-embossed metal foilor a combination of these materials.
 8. Lids according to claim 7,characterised in that the substrate material containing a combination ofat least one thermoplastic and/or a cellophane and/or acellulose-containing material and/or a metal foil in the form of amulti-layer non-embossed composite material.
 9. Lids according to claim8, characterised in that the substrate material contains a barrier layeragainst gases, vapours and moisture in the form of a ceramic layer or ametallised layer or a plastic film or a metal foil.
 10. Lids accordingto claim 8, characterised in that the sealing layer exhibits a weightper unit area of 30 g/m² and less, usefully from 2 to 20 g/m²,advantageously from 2 to 15 g/m², in particular from 5 to 10 g/m². 11.Lids according to claim 10, characterised in that the sealing layer is aco-extrudate containing a bonding agent in the form of an extrusionlayer having a weight per unit area of 2 to 10 g/m², usefully from 2 to8 g/m², and an extrusion layer of thermoplastic having a weight per unitarea of 3 to 25 g/m², in particular from 5 to 10 g/m².
 12. Process formanufacturing lids for closing off containers using a sealing seam,where the lids contain a substrate material featuring, with respect to acontainer on which the lids are used, an outward facing printing and aninward facing sealing layer, characterised in that, the substratematerial is coated via an extrusion coating or co-extrusion coating withan extrusion layer or co-extrusion layer forming the sealing layer, andthe coated substrate material is passed between a pressure roll and acooling roll while being put under pressure, whereby the substratematerial faces the pressure roll and the extrusion layer or co-extrusionlayer faces the cooling roll, and the configuration of the surface ofthe cooling roll transfers to the extrusion layer or co-extrusion layeras a reverse image forming an embossed sealing layer.
 13. Process formanufacturing lids according to claim 12, characterised in that thecooling layer exhibits as surface configuration a roughness patternhaving a depth of roughness of up to 50 μm, usefully from 3 to 30 ∥m,advantageously from 3 to 20 μm, in particular 5 to 10 μm.